Various catalysts which substitute fluorine atoms for chlorine atoms have been proposed for use in gaseous phase reactions. Frequently, these catalysts are oxides or halides of chromium, aluminum, cobalt, iron, titanium, nickel, copper, palladium or zirconium; which may be supported on active carbon or alumina. U.S. Pat. No. 2,458,551, for example, describes catalysts having a chromium trifluoride base deposited on active carbon or calcium fluoride.
U.S. Pat. No. 3,258,500 discloses a non-supported anhydrous trivalent chromium oxide catalyst prepared by the reduction of chromium trioxide and subsequent heating of the reduced product at a temperature of 400.degree.-600.degree. C.
British Pat. No. 896,068 and U.S. Pat. No. 3,157,707 describe alumina-supported chromium oxide catalysts prepared by the reduction of chromium trioxide by hydrogen. The catalysts are useful in the preparation of fluorinated compounds such as trichlorotrifluoroethane, dichlorotetrafluoroethane from hexachloroethane.
U.S. Pat. No. 2,892,000 discloses the preparation of vinyl fluoride and 1,1-difluoroethane by reacting hydrogen fluoride with acetylene in the presence of a catalyst comprising chromium oxide or chromium salt.
Other patents such as Japanese Application Nos. 70.116696 and 74.131610, teach the reduction of chromium trioxide by aldehydes or hydrazine, for the preparation of catalysts.
These commonly used chromium halide catalysts deposited on carbon supports are basically suitable for gaseous phase fluorination of chloroalkanes or chlorofluoroalkanes in fixed bed reactor systems. In fluidized bed reactors, which require regular-shaped particles and homogeneous granulometry, the prior art catalysts are inadequate and inefficient for use in fluorination processes. Simple grinding of the catalysts, followed by sifting for the selection of suitable-sized particles provides irregularly-shaped grains which are not suitable for use in fluidized bed reactors. Consequently, their use leads to a significant loss of the catalyst, which necessitates recharging the reactor at various intervals during the process.
The prior art catalysts often demonstrate at least one of the following disadvantages:
low rate of conversion of hydrofluoric acid PA1 low productivity PA1 low selectivity PA1 a high level of asymmetric isomers in the production of trichlorotrifluoroethane and dichlorotetrafluoroethane.